Avaliação no ATPDraw das proteções diferencial e de sobrecorrente aplicadas a um transformador de potência

Abstract

This work analyzed the differential and overcurrent protections in ATPDraw for a YDn1 power transformer, with the high-voltage side connected in a grounded wye configuration and the low-voltage side in delta. The protections were implemented in ATPDraw with differential protection blocks (87T), instantaneous overcurrent (50), and time-delayed overcurrent (51). Phase overcurrent functions (50F/51F) and neutral overcurrent functions (50N/51N) were incorporated on the high-voltage side. In 87T block of ATPDraw, it was necessary to include the zero-sequence compensation and angular correction. Faults were simulated on the transformer’s busbars and bushings, covering conventional and internal faults caused by short circuits turn-to-turn and turnto-ground. The 50F and 51F functions demonstrated effectiveness and selectivity in responding to faults on the bushings and busbars. The 50N and 51N functions operate to ground faults, except for those on the low-voltage side, as the delta connection prevents the high-voltage side from contributing to zero-sequence components generated by ground faults. Additionally, the 50N and 51N functions responded quickly to turn-to-ground short circuits in the grounded wye configuration. However, none of the overcurrent functions could defect turn-to-turn or turn-to-ground faults on the delta-connected windings. The differential protection 87T, with zero-sequence compensation and angular correction, performed well for faults on the busbars and bushings. However, it required a high percentage of short-circuited turns on the low-voltage side to operate, specifically 90% for turn-to-ground short circuits and 65% for turn-to-turn short circuits. Therefore, it was recommended that the relay sensitivity be increased by adjusting the slope of the second region to enhance fault detection on the delta side.